Fenton R G, Basilico C
J Virol. 1981 Oct;40(1):150-63. doi: 10.1128/JVI.40.1.150-163.1981.
We have studied transcription of integrated viral DNA sequences in a variety of ts-a polyoma virus-transformed rat cells and cured revertants (which had undergone excision of variables amounts of integrated viral DNA) to characterize the structure of viral mRNA's produced in these lines under conditions in which integrated DNA is stable. Our results indicate that cells containing intact early region sequences, either in single-copy or tandem insertions, produce mRNA's indistinguishable from those observed early in lytic infections; sequences complementary to the polyoma late region were not transcribed from integrated viral DNA. Cured revertants no longer encoded full-length early mRNA's , but produced viral transcripts whose 3' ends mapped at an alternative early region polyadenylic acid attachment site at 99 map units or extended in to flanking host sequences. The phenotype of these revertant cells correlated with the abundance of these transcripts, suggesting that the transforming function(s) of polyoma virus controls the cellular phenotype in a dose-dependent manner. Unexpected results were obtained from studies of cells containing tandem repeats of defective viral DNA in which the polyadenylic acid attachment signal at 25.8 map units and surrounding sequences were deleted. In these cases, polyadenylated mRNA's were observed that contained sequences complementary to the early strand of the polyoma late region. These mRNA's (some larger than 8 kilobases) originated at the viral early promoter, extended into the late region, and continued into the early region of the contiguous repeat in the tandem. The multimeric mRNA's produced contained defective early regions in tandem with late region sequences. S1 analysis indicated that whereas the 5' early region sequences of readthrough transcripts were spliced in the usual manner, internal early region repeats were either unspliced or used only one of the small early region splices. When deletions in the viral readthrough transcripts were observed. This suggests that sequences nearby the AAUAAA sequence at 26 map units may control transcription termination of the polyoma early region.
我们研究了多种ts-a多瘤病毒转化的大鼠细胞以及治愈的回复突变体（已切除不同数量整合病毒DNA）中整合病毒DNA序列的转录情况，以表征在整合DNA稳定的条件下这些细胞系中产生的病毒mRNA的结构。我们的结果表明，含有完整早期区域序列的细胞，无论是单拷贝还是串联插入，产生的mRNA与溶细胞感染早期观察到的mRNA无法区分；与多瘤晚期区域互补的序列未从整合病毒DNA转录。治愈的回复突变体不再编码全长早期mRNA，但产生病毒转录本，其3'末端定位于99个图谱单位处的另一个早期区域聚腺苷酸附着位点，或延伸至侧翼宿主序列。这些回复突变体细胞的表型与这些转录本的丰度相关，表明多瘤病毒的转化功能以剂量依赖方式控制细胞表型。对含有缺陷病毒DNA串联重复序列的细胞进行研究时获得了意外结果，其中25.8个图谱单位处的聚腺苷酸附着信号及周围序列被删除。在这些情况下，观察到了多聚腺苷酸化的mRNA，其包含与多瘤晚期区域早期链互补的序列。这些mRNA（有些大于8千碱基）起源于病毒早期启动子，延伸至晚期区域，并继续进入串联中相邻重复序列的早期区域。产生的多聚体mRNA包含与晚期区域序列串联的缺陷早期区域。S1分析表明，通读转录本的5'早期区域序列以通常方式剪接，而内部早期区域重复序列要么未剪接，要么仅使用了一个小的早期区域剪接。当观察到病毒通读转录本中的缺失时。这表明26个图谱单位处AAUAAA序列附近的序列可能控制多瘤早期区域的转录终止。
